1. Field of the Invention
The present invention relates to a position detecting apparatus configured to detect a position of a moving member with respect to a fixed member. In particular, the present invention relates to a position detecting apparatus using both an absolute encoder and a relative encoder that use a sensor configured to output a plurality of phase signals while switching the plurality of phase signals in time series, and to a lens apparatus and an optical operating apparatus using the position detecting apparatus.
2. Description of the Related Art
In an optical apparatus and accessories thereof, there is an increasing demand for a function that allows use immediately after power-on in order to secure a photo opportunity. Further, an optical apparatus using a relative encoder in order to obtain positional information on a movable member of the apparatus needs to be initialized, and therefore cannot be used immediately after the power-on of the apparatus or consumes electric power for the initialization, which has increased the use of an absolute encoder. However, the absolute encoder necessitates more complicated calculation than the relative encoder does, and hence there is disclosed a technology for AD-converting a plurality of sensor outputs simultaneously in order to reduce a delay in the calculation. Further, there are disclosed a technology for detecting an abnormality due to a data retrieval error and a technology for realizing power saving or taking measures against a retrieval error by using a combination of the absolute encoder and the relative encoder.
In Japanese Patent Application Laid-Open No. H05-45151, there is disclosed a technology in which, because a slider of a digital caliper is in a stopped state for most of the time, an absolute counting unit is stopped and an incremental counting unit is operated when the slider is moving at a low speed or is stopped. In addition, when the slider is moving at high speed, the absolute counting unit is operated while the incremental counting unit is stopped.
In Japanese Patent Application Laid-Open No. 2005-345375, there is disclosed a technology in which an absolute position is obtained at power-on, and after that, incremental counting is conducted by only a minute scale, or an absolute value and a relative value are alternately obtained, to thereby increase reliability.
The absolute encoder necessitates more complicated calculation than the relative encoder does, and therefore can cause a problem in that processing is delayed when a lens, an operation unit, or the like moves at high speed. To cope therewith, it is necessary to increase a sampling frequency, mount a plurality of phase detection circuits in order to simultaneously process phase outputs of an encoder, and mount a high-performance CPU in order to execute complicated calculation processing at high speed. Therefore, there is a problem of causing an increase in current consumption and in cost. Further, there is another problem of causing an increase in the electric power and in cost due to providing of a calculation unit and a phase output unit for detecting an error in the absolute encoder. Further, in a case where a control subject moves at a remarkably high speed also in the processing of the relative encoder, a count error occurs when phase output signals corresponding to at least two cycles exist within a sampling cycle and hence, it is necessary to increase the sampling cycle.
On the other hand, in regard to a lens used for a camera, a zoom lens and a focus lens are rarely used for photographing in a fixed position, and are often moved in accordance with a photographic scene. Further, to move an optical system at high speed, it is not necessary to attain accuracy for a position of the optical system to be detected. For example, when the zoom lens needs to be moved at high speed, the zoom lens is used for transition of a scene (transition: shifting from a given scene to another scene), but is not used for the purpose of a picture (the shot image taken during the transition with high-speed zooming is not generally used for visual expression). To obtain focus by moving the focus lens at high speed, the picture is blurred while the focus lens is being moved to the vicinity of an in-focus position, which lowers importance as the picture. In contrast, the focus lens is moved at a low speed near the in-focus position in order to obtain focus with precision.
Further, the same applies to position detection of an operation unit such as a zoom demand or a focus demand during an operation of the operation unit.